Much of the world's natural gas supply is contaminated with unacceptably high levels of carbon dioxide (CO2). In some cases, in addition to excessive CO2, the natural gas may also contain excessive levels of sulfur compounds. Such sulfur compounds include hydrogen sulfide and carbonyl sulfide. In many cases, the carbon dioxide and sulfur contaminants lower the BTU value of natural gas making such gas unsuitable for use as a fuel or unsuitable to be transported in a pipeline carrier. Various commercial technologies including low temperature distillation, amine scrubbing and membrane separation, have been developed to upgrade natural gas containing excessive CO2 or sulfur compounds. All of the above-mentioned technologies typically produce a useable natural gas stream and a carbon dioxide/sulfur compound stream. The distillation separation of CO2 from hydrocarbon gas is a very energy and capital-intensive process. The present invention is an improvement on distillation technology that reduces the energy and capital requirement, producing a hydrocarbon product more efficiently.
Background information relating to the extraction of CO2, with or without accompanying sulfur compounds, from hydrocarbon gas may be found in the following publications:    (1) Process Can Efficiently Treat Gases Associated With CO2 Miscible Flood—Oil & Gas Journal, Jul. 18, 1983.    (2) U.S. Pat. No. 4,936,887—Distillation Plus Membrane Processing of Gas Streams, Waldo et al., Jun. 26, 1990.    (3) Canadian Patent No. 1,253,430—Process and Apparatus for Fractionation of a Gaseous Mixture, Burr, May 2, 1989.    (4) U.S. Pat. No. 4,417,449—Process for Separating Carbon Dioxide and Acid Gases From a Carbonaceous Off-Gas, Hagarty et al., Nov. 29, 1983.    (5) U.S. Pat. No. 4,602,477—Membrane-Aided Distillation for Carbon Dioxide and Hydrocarbon Separation, Lucadamo, Jul. 29, 1986.    (6) U.S. Pat. No. 4,444,571—Energy Efficient Process for the Stripping of Gases from Liquids, Matson, Apr. 24, 1984.    (7) U.S. Pat. No. 4,374,657—Process of Separating Acid Gases from Hydrocarbons, Feb. 22, 1983.